@misc{cryptoeprint:2007:272,
author = {Willi Geiselmann and Rainer Steinwandt},
title = {Cryptanalysis of a Hash Function Proposed at ICISC 2006},
howpublished = {Cryptology ePrint Archive, Report 2007/272},
year = {2007},
note = {\url{http://eprint.iacr.org/}},
}
You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.